An NHS trust that has banned obese people from undergoing hip and knee replacement surgery is considering barring its staff from smoking in public even when they are not on its premises, it emerged today.

Suffolk East primary care trust (PCT), the body that runs local community health services, face being banned from smoking while wearing their uniform or ID badge - even when they are not at work.

The PCT's board is due to decide whether to approve the new smoking policy on Wednesday, but public services union Unison has branded it "unworkable" and "unenforceable".

The policy states that staff must not smoke in a public place if they can be identified as an employee of the trust. This means they would not be able to smoke on other premises where smoking is permitted.

Smoking will also not be allowed in the PCT's leased and pool cars, except where the driver contributes to the lease cost for personal use of the vehicle. Even then, it will only be allowed in non-work time. The policy does not apply to privately owned vehicles except when they are on PCT premises or are being used on PCT business.

The PCT chief executive, Carole Taylor-Brown, has issued a policy statement directing that the organisation's buildings, vehicles and outside grounds will be smoke-free. The policy applies to all staff, volunteers, patients, visitors, contractors and any other people who enter PCT premises for any purpose.

A report to the PCT board states: "The cessation of smoking in all the PCT's environments (including the grounds of all establishments) will improve their appearance as cigarette butts will disappear from underfoot and the pall of smoke around entrances to buildings will dissipate."

If the policy is approved by the board, there will be a three-month lead-in period in which staff will be encouraged to comply. After that, a breach will result in disciplinary action.

Ian Talbot, Suffolk healthcare Unison branch secretary, warned that the move could force smokers underground, causing health and safety risks.

He told the East Anglian Daily Times: "It's just absolute rubbish, the whole thing, from start to finish. It's unenforceable. If somebody is on their own break time and if they are going to work in their own vehicle, they are saying they can't actually smoke in their vehicle in the car park."

"The union is in favour of smoke-free, but not the way that policy is written. It's unworkable. This will go down like a lead balloon."

Mr Talbot said some smokers could end up smoking in cupboards or toilets to avoid detection. "All it will be is to have smoking underground and you'll probably actually find there's more fire risk."

Last week it emerged that obese people are not be entitled to hip and knee replacement surgery on the NHS in East Suffolk until they lose weight.